That's totally allowed and I'm glad you asked it as I'm sure it's something a lot of people have encountered. As mentioned by everyone else HTML on IJ (and many other journal sites) is different from that of a webpage. On a normal webpage, it treats the site like there are no spaces between lines (so, you have to use paragraphs [p][/p] and breaks [br /] - with the correct punctuation, as trysola said). On IJ this isn't the case in hopes of making it easier on users. So, when you press enter, the motion is treated like having entered [p][/p] or [br /].